Karyotype Tests

Medically Reviewed by Amita Shroff, MD on August 30, 2022
Written by WebMD Editorial Contributors
4 min read

Karyotype tests take a close look at the chromosomes inside your cells to see if anything about them is unusual. They’re often done during pregnancy to spot problems with the baby. This type of procedure is also referred to as genetic or chromosome testing, or cytogenetic analysis.  

When you’re pregnant, the doctor will want to do several prenatal screening tests that look for certain genetic and chromosomal disorders. You’ll probably be offered one during your first trimester and another in your second trimester.

Most women get results that are within the normal range and don’t need any further tests. But if any of your screening tests show signs of a problem, the doctor will offer you follow-up tests so you can find out for sure whether your growing baby has any genetic or chromosomal problems.

Humans have 46 chromosomes. Babies inherit 23 from their mom and 23 from their dad.

Sometimes, babies have an extra chromosome, a missing chromosome, or an abnormal chromosome. Karyotype tests will see if any of these have happened with your baby. The most common things doctors look for with karyotype tests include:

  • Down syndrome (trisomy 21). A baby has an extra, or third, chromosome 21. This affects how the baby looks and learns.
  • Edwards syndrome (trisomy 18). A baby has an extra 18th chromosome. These babies usually have many problems, and most don’t live longer than a year.
  • Patau syndrome (trisomy 13). A baby has an extra 13th chromosome. These babies usually have heart problems and severe mental impairment. Most won’t live more than a year.
  • Klinefelter syndrome. A boy baby has an extra X chromosome (XXY). They may go through puberty at a slower pace, and may not be able to have children.
  • Turner syndrome. A girl baby has a missing or damaged X chromosome. It causes heart problems, neck problems, and short height.

Karyotype tests can be used for more than finding birth defects.

  • If you’ve had trouble getting pregnant or have had several miscarriages, the doctor may want to check whether you or your partner have a chromosome problem.
  • You can find out if you have a disorder that you could pass down to your child.
  • They can test a stillborn baby to see if there was a genetic issue.
  • They can find the cause of certain physical or developmental problems your baby or young child has.
  • Chromosome tests can show whether a newborn is a boy or a girl in the rare cases where it isn’t clear.  
  • Certain kinds of cancer can cause chromosome changes. Karyotype testing can help get you the right treatment. 

Karyotype tests can only be performed during certain weeks of your pregnancy. Your doctor will suggest which karyotype test is right for you based on how far along you are in your pregnancy and on your risks.

It’s more likely your baby could have a chromosome problem if:

  • You’re 35 or older.
  • You have another child or a family member who has a chromosome disorder.
  • You or your partner have something unusual in your chromosomes.
  • You have a history of miscarriages or had a baby that was stillborn.

The tests include:

Chorionic villus sampling (CVS). Doctors use a long needle to remove a small sample of your baby’s cells from the chorionic villi, which are tissues in the placenta (the organ that forms within your womb to nourish your growing baby).

Doctors send these cells to a lab for more testing. Results can show whether or not your baby has Down syndrome, trisomy 13, trisomy 18, or other genetic problems.

If the doctor says you need CVS, you can have it done between 10 and 13 weeks. There’s a chance it could lead to miscarriage. It happens to 1 out of every 100 women who get the test. There’s also some risk to the baby, so doctors only suggest it if there’s a good chance your baby has a problem.

Amniocentesis. Doctors get samples of your baby’s cells by taking a small amount of amniotic fluid (the liquid that surrounds your baby in the womb) with a long needle they stick through your abdomen. They send the cells to a lab for more testing.

Test results can show whether your baby has any of the genetic problems that the CVS testing can find, as well as some neural tube defects, which are severe problems that can affect your baby’s brain or spine.

If the doctor says you need amniocentesis, you can have it done between 15 and 20 weeks. There’s a chance you could miscarry, but it’s a smaller chance than with CVS. It happens to just 1 out of every 200 women who have the procedure.

Bone marrow aspiration and biopsy. If you’re getting a chromosome test because you have cancer or a blood disorder, the doctor may need to use a bone marrow sample. They usually take it from your hip bone with a special needle while you’re numb but awake.

The procedures used to gather cells for karyotype testing do have some risks. It’s possible for CVS or amniocentesis to cause a miscarriage. You might also have heavy bleeding or get an infection from a bone marrow aspiration and biopsy.

When the lab sends your results back, they’ve looked at your baby’s chromosomes, so the results are definite: Either your baby has a genetic problem or they don’t.

This is different from earlier screening tests, which could only say there’s a high or low chance of a problem. Your doctor will discuss the test results with you.